I've always been fascinated by the impact of various drug-containing plants on humanity and it's history. Plants, because most drugs are extracted or synthesised from them.
Shamans say that it is the 'essence' or 'spirit' of the plant that is psychoactive - you're 'inviting' another 'being' into your consciousness.
Those who smoked pot have probably noticed the alternative or alien 'voice' which appears in your head and makes you think and say funny things or think paranoid thoughts. This happens with all drugs - the drug (or, in shamanic terms - the spirit of the plant) becomes one's invisible councillor - an interlocutor in the user's internal dialogue.
Take tobacco - the act of smoking a cigarette is an act of 'conversing' with the plant, an act of thinking and taking decisions. Notice the impact that tobacco has had on the development of the human race - it's impossible to claim that it was responsible for all our progress, but somehow it was present in the pipes of Einstein and Oppenheimer and in the cigars smoked after a successful space mission.
It was also present in the trenches of wars.
Today our world is more drugged than it has ever been. Besides all the classes of illegal drugs, we also have people eating tens of thousands of various synthetic chemicals - prescription drugs - and of course making all sorts of combinations between them.
What will the consequence of this chemical experimentation end up being ?
Time will tell. Clearly we're doing some radical changes to how our minds and bodies work and this has a direct impact on how our society looks and behaves and what decisions are being made.